1. Field of the Invention
The present invention relates to a semiconductor device including a semiconductor substrate with a collector layer formed thereon, and to a method of manufacturing such a semiconductor device.
2. Background Art
Japanese Laid-Open Patent Publication No. 2004-311481 discloses a semiconductor device including a collector layer in contact with a collector electrode. The collector layer has a carrier concentration profile or distribution having a peak value at a position proximate to the collector electrode, and the collector layer and the collector electrode are in ohmic contact with each other. It should be noted that the term “carrier concentration peak position” is hereinafter used to refer to a position where a carrier concentration profile has a peak value.
In order to reduce the switching loss of a semiconductor device, it is known practice to reduce the level of the carrier concentration at the carrier concentration peak position in the collector layer. This means, however, that the carrier concentration at the carrier concentration peak position is more likely to be affected by contamination in the manufacturing atmosphere. It was found that the carrier concentration at the carrier concentration peak position was affected by contamination in the manufacturing atmosphere to such an extent that the manufactured semiconductor devices did not have the desired characteristics or varied in characteristics.